Iatrogenic neuromuscular disorders: A review

Abstract

The diagnosis of a drug-induced neuromuscular disorder can usually be suspected from the clinical features, particularly from the history of drug exposure. Drug-induced neuropathies usually present with dysaesthesiae in the distal parts of the limbs, but weakness may be only slight; the distal tendon reflexes are invariably diminished or absent. The diagnosis can be confirmed by motor and sensory nerve conduction studies (Swash & Schwartz 1981) and by the improvement which slowly occurs when the offending drug is withdrawn. Drug-induced disturbances of neuromuscular transmission may be mild, or severe enough to cause embarrassment. The response to intravenous edrophonium will usually confirm the diagnosis; electrophysiological studies using repetitive nerve stimulation or single fibre electromyography (Swash & Schwartz 1981) are particularly useful in mild cases. The presence of underlying myasthenia gravis, enhanced by the drug, can be confirmed by measuring circulating acetylcholine receptor antibody levels (Lindstrom et al. 1976). Drug-induced myopathies are often associated with increased blood creatine kinase levels. Electrolyte disturbances, particularly hypokalaemia, should always be considered. Myoglobulinuria may occur when there is acute severe muscle necrosis. In certain circumstances, e.g. steroid myopathy, when anaesthetic drugs are used in myasthenic patients or when isoniazid is used in tuberculosis, the development of a neuromuscular complication can be predicted and appropriate measures taken. A full drug history is an important part of the evaluation of any patient presenting with neuromuscular symptoms.